feat(app): implement resource download + 'open with' dialog

Closes #123

app/src/main/java/de/bollwerk/app/ui/resources/ResourceListScreen.kt

@@ -1,5 +1,8 @@
 package de.bollwerk.app.ui.resources
 
+import android.content.ActivityNotFoundException
+import android.content.Context
+import android.content.Intent
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
@@ -11,6 +14,7 @@ import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.height
 import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
 import androidx.compose.foundation.layout.width
 import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.items
@@ -29,11 +33,14 @@ import androidx.compose.material3.IconButton
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.OutlinedTextField
 import androidx.compose.material3.Scaffold
+import androidx.compose.material3.SnackbarHost
+import androidx.compose.material3.SnackbarHostState
 import androidx.compose.material3.Surface
 import androidx.compose.material3.Text
 import androidx.compose.material3.TextButton
 import androidx.compose.material3.TopAppBar
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
@@ -41,11 +48,14 @@ import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.unit.dp
+import androidx.core.content.FileProvider
 import androidx.hilt.navigation.compose.hiltViewModel
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import de.bollwerk.shared.model.ResourceDto
+import java.io.File
 
 @OptIn(ExperimentalMaterial3Api::class, ExperimentalLayoutApi::class)
 @Composable
@@ -54,6 +64,8 @@ internal fun ResourceListScreen(
 ) {
     val uiState by viewModel.uiState.collectAsStateWithLifecycle()
     var isSortMenuExpanded by remember { mutableStateOf(false) }
+    val snackbarHostState = remember { SnackbarHostState() }
+    val context = LocalContext.current
 
     val filteredResources = remember(
         uiState.resources,
@@ -77,6 +89,25 @@ internal fun ResourceListScreen(
             }
     }
 
+    // Handle download state changes (open file on success, show error snackbar)
+    uiState.downloadStates.forEach { (guid, state) ->
+        when (state) {
+            is DownloadState.Success -> {
+                LaunchedEffect(guid, state) {
+                    openFile(context, state.file, state.mimeType, snackbarHostState)
+                    viewModel.clearDownloadState(guid)
+                }
+            }
+            is DownloadState.Error -> {
+                LaunchedEffect(guid, state) {
+                    snackbarHostState.showSnackbar("Download fehlgeschlagen")
+                    viewModel.clearDownloadState(guid)
+                }
+            }
+            else -> {}
+        }
+    }
+
     Scaffold(
         topBar = {
             TopAppBar(
@@ -90,7 +121,8 @@ internal fun ResourceListScreen(
                     }
                 }
             )
-        }
+        },
+        snackbarHost = { SnackbarHost(snackbarHostState) }
     ) { padding ->
         Column(
             modifier = Modifier
@@ -182,7 +214,19 @@ internal fun ResourceListScreen(
                         verticalArrangement = Arrangement.spacedBy(8.dp)
                     ) {
                         items(filteredResources, key = { it.guid }) { resource ->
-                            ResourceCard(resource = resource)
+                            val downloadState = uiState.downloadStates[resource.guid] ?: DownloadState.Idle
+                            ResourceCard(
+                                resource = resource,
+                                downloadState = downloadState,
+                                onDownloadClick = {
+                                    viewModel.downloadAndOpen(
+                                        guid = resource.guid,
+                                        mimeType = resource.mimeType,
+                                        fileFormat = resource.fileFormat,
+                                        context = context
+                                    )
+                                }
+                            )
                         }
                     }
                 }
@@ -193,7 +237,11 @@ internal fun ResourceListScreen(
 
 @OptIn(ExperimentalLayoutApi::class)
 @Composable
-private fun ResourceCard(resource: ResourceDto) {
+private fun ResourceCard(
+    resource: ResourceDto,
+    downloadState: DownloadState,
+    onDownloadClick: () -> Unit
+) {
     Card(
         modifier = Modifier.fillMaxWidth()
     ) {
@@ -209,13 +257,23 @@ private fun ResourceCard(resource: ResourceDto) {
                     fontWeight = FontWeight.Bold,
                     modifier = Modifier.weight(1f)
                 )
-                IconButton(onClick = { /* download handled externally */ }) {
+                IconButton(
+                    onClick = onDownloadClick,
+                    enabled = downloadState !is DownloadState.Loading
+                ) {
+                    if (downloadState is DownloadState.Loading) {
+                        CircularProgressIndicator(
+                            modifier = Modifier.size(24.dp),
+                            strokeWidth = 2.dp
+                        )
+                    } else {
                         Icon(
                             imageVector = Icons.Filled.Download,
                             contentDescription = "Herunterladen"
                         )
                     }
                 }
+            }
 
             Row(
                 horizontalArrangement = Arrangement.spacedBy(8.dp),
@@ -283,3 +341,21 @@ private fun formatFileSize(bytes: Long): String {
         String.format("%.0f KB", bytes / 1024.0)
     }
 }
+
+private suspend fun openFile(
+    context: Context,
+    file: File,
+    mimeType: String,
+    snackbarHostState: SnackbarHostState
+) {
+    val uri = FileProvider.getUriForFile(context, "${context.packageName}.fileprovider", file)
+    val intent = Intent(Intent.ACTION_VIEW).apply {
+        setDataAndType(uri, mimeType)
+        addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION)
+    }
+    try {
+        context.startActivity(intent)
+    } catch (_: ActivityNotFoundException) {
+        snackbarHostState.showSnackbar("Keine App zum Öffnen dieser Datei gefunden")
+    }
+}

app/src/main/java/de/bollwerk/app/ui/resources/ResourceListViewModel.kt

@@ -1,15 +1,19 @@
 package de.bollwerk.app.ui.resources
 
+import android.content.Context
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import dagger.hilt.android.lifecycle.HiltViewModel
 import de.bollwerk.app.domain.repository.ResourceRepository
 import de.bollwerk.shared.model.ResourceDto
+import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.asStateFlow
 import kotlinx.coroutines.flow.update
 import kotlinx.coroutines.launch
+import kotlinx.coroutines.withContext
+import java.io.File
 import javax.inject.Inject
 
 internal enum class SortMode(val label: String) {
@@ -18,13 +22,21 @@ internal enum class SortMode(val label: String) {
     SIZE_DESC("Größe groß→klein")
 }
 
+internal sealed interface DownloadState {
+    data object Idle : DownloadState
+    data object Loading : DownloadState
+    data class Success(val file: File, val mimeType: String) : DownloadState
+    data class Error(val message: String) : DownloadState
+}
+
 internal data class ResourceListUiState(
     val resources: List<ResourceDto> = emptyList(),
     val searchQuery: String = "",
     val selectedTags: Set<String> = emptySet(),
     val sortMode: SortMode = SortMode.TITLE_ASC,
     val isLoading: Boolean = false,
-    val allTags: List<String> = emptyList()
+    val allTags: List<String> = emptyList(),
+    val downloadStates: Map<String, DownloadState> = emptyMap()
 )
 
 @HiltViewModel
@@ -74,4 +86,35 @@ internal class ResourceListViewModel @Inject constructor(
     fun setSortMode(mode: SortMode) {
         _uiState.update { it.copy(sortMode = mode) }
     }
+
+    fun downloadAndOpen(guid: String, mimeType: String, fileFormat: String, context: Context) {
+        viewModelScope.launch {
+            _uiState.update { state ->
+                state.copy(downloadStates = state.downloadStates + (guid to DownloadState.Loading))
+            }
+            try {
+                val bytes = resourceRepository.downloadResource(guid)
+                val file = withContext(Dispatchers.IO) {
+                    File(context.cacheDir, "$guid.$fileFormat").also { it.writeBytes(bytes) }
+                }
+                _uiState.update { state ->
+                    state.copy(
+                        downloadStates = state.downloadStates + (guid to DownloadState.Success(file, mimeType))
+                    )
+                }
+            } catch (e: Exception) {
+                _uiState.update { state ->
+                    state.copy(
+                        downloadStates = state.downloadStates + (guid to DownloadState.Error(e.message ?: "Unbekannter Fehler"))
+                    )
+                }
+            }
+        }
+    }
+
+    fun clearDownloadState(guid: String) {
+        _uiState.update { state ->
+            state.copy(downloadStates = state.downloadStates + (guid to DownloadState.Idle))
+        }
+    }
 }

app/src/main/res/xml/file_paths.xml

@@ -9,4 +9,7 @@
     <cache-path
         name="update"
         path="update/" />
+    <cache-path
+        name="downloads"
+        path="." />
 </paths>